The present invention is directed to a milling machine for cutting the side bearing pads of a railcar truck bolster. More particularly, the present invention is directed to a milling machine that is capable of precisely and repeatedly machining the side bearing mounting pads of a cast railcar truck bolster.
A railcar rides on and is supported by what is known as a railcar truck. Commonly, there are two trucks per railcar. Each truck generally includes two elongated and transversely spaced side frames that rest on corresponding wheel sets provided to engage a set of train tracks. An elongated truck bolster (bolster) typically extends substantially perpendicularly between, and is connected to, the pair of side frames. Normally, the bolster is supported on the side frames by a number of springs that serve to provide the railcar and its cargo with a cushioned ride. The springs reside between the side frames and a spring seat area on the underside of the bolster.
The bolster connects each truck to the railcar, and is generally provided on its top surface with a connecting member for this purpose. The bolster is also provided on its top surface with a pair of side bearing mounting pads that are normally substantially equidistantly spaced from and reside on opposite sides of the midpoint of the bolster. The side bearing mounting pads are provided to receive a shock absorbing side bearing assembly that resists and cushions rocking of the railcar as it negotiates curves and/or traverses bumpy sections of track.
Railcar bolsters are typically cast members. As such, certain areas of such a bolster, such as those designed to receive mating components or to fit precisely with another truck or railcar element, will typically require machining after casting. Such is the case with the side bearing mounting pads.
The side bearing mounting pads serve not only to secure the side bearing assemblies to the bolster, but also to locate the side bearing assemblies with respect to the underside of the railcar. As such, it is desired not only that the side bearing mounting pads be machined to a flat and level surface, but also that they be machined to a precise height with respect to some reference point or surface on the bolster. This is desired to ensure that the side bearing assembly will properly contact the underside of the railcar once the railcar has been secured to the truck. For example, if an excessive amount of material is removed from a side bearing mounting pad, there may be a gap between the side bearing assembly affixed thereto and the underside of the railcar—which may lead to an undesirable impacting of the railcar with the side bearing assembly when the railcar negotiates curves or encounters a rough section of track. In contrast, the removal of an inadequate amount of material from a side bearing mounting pad may make it difficult or impossible to properly fit the side bearing assembly between the top of the bolster and the underside of the railcar.
Known machines for milling railcar bolster side bearing mounting pads have proven incapable of continually providing precise and repeatable results. Rather, wear problems inherent to the design of these known machines eventually causes the side bearing mounting pads to be machined out of tolerance—unless certain components of the machines are frequently replaced, or the bolsters are shimmed or otherwise manipulated into proper position when in the machines.
More specifically, known railcar side bearing mounting pad milling machines typically raise the bolster into a working position for engagement by a milling head(s) and associated cutter(s). The bolster is typically raised to a predetermined position and held in place, commonly against a stop, while the cutters machine the side bearing mounting pads. This technique is problematic for multiple reasons. First, both gravity and the downward pressure exerted by the milling heads against the side bearing mounting pads act against the lifting mechanism responsible for raising the bolster. Thus, it is difficult to maintain the bolster in the exact position necessary to allow for milling the pads precisely to the required depth. Second, repeated impact between the top surface of the bolster and the overlying hard stops produces excessive wearing of the hard stops. Any wear of the hard stops will, of course, allow the side bearing mounting pads to be located to an incorrect height with respect to the milling heads. Further, the hard stops may experience dissimilar amounts of wear, thereby allowing the side bearing mounting pads to be milled to different heights.
Consequently, it can be understood that there is a need for an apparatus that is better able to ensure that the side bearing mounting pads are always precisely and repeatedly located prior to the machining thereof. A side bearing milling machine of the present invention satisfies this need.